Scale client area, hit test mask and bounds by device_scale_factor.

services/ui/test_wm/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//services/service_manager/public/cpp/service.gni")
 import("//services/service_manager/public/service_manifest.gni")
 
 service("test_wm") {
+  testonly = true
+
   sources = [
     "test_wm.cc",
   ]
 
   deps = [
     "//base",
     "//services/service_manager/public/cpp",
     "//services/ui/public/cpp",
     "//services/ui/public/interfaces",
     "//ui/display",
+    "//ui/display:test_support",
     "//ui/gfx/geometry/mojo",
   ]
 
   data_deps = [
     ":manifest",
     "//services/ui",
   ]
 }
 
 service_manifest("manifest") {
   name = "test_wm"
   source = "manifest.json"
 }